Carbonic Anhydrase Enhanced Reaction Methods and Formulations

ABSTRACT

Disclosed is a formulation for the absorption of CO 2 , which comprises water, at least one CO 2  absorption compound and a carbonic anhydrase as an activator to enhance the absorption capacity of the CO 2  absorption compound. The invention also concerns the use of carbonic anhydrase, in a CO 2  absorption solution to increase the CO 2  absorption rate of such solution.

FIELD OF THE INVENTION

The present invention relates generally to solutions for absorbing CO₂for extraction and purification of gases. More particularly, it relatesto a CO₂ absorption solution containing a biocatalyst, namely carbonicanhydrase as an activator, to increase CO₂ absorption rate. It alsoconcerns the use of a biocatalyst, namely carbonic anhydrase, in a CO₂absorption solution to increase the CO₂ absorption rate of suchsolution.

BACKGROUND OF THE INVENTION

CO₂ removal from a gas stream may be obtained using chemical andphysical absorption processes. Chemical absorption of CO₂ may beperformed with amine based processes and alkaline salt-based processes.In such processes, the absorbing medium reacts with the absorbed CO₂.Amines may be primary, secondary, and tertiary. These groups differ intheir reaction rate, absorption capacity, corrosion, degradation, etc.In alkaline salt-based processes, the most popular absorption solutionshave been sodium and potassium carbonate. As compared to amines,alkaline salt solutions have lower reaction rates with CO₂.

Alkanolamines in aqueous solution are another class of absorbent liquidfor carbon dioxide removal from gaseous mixtures. Alkanolamines areclassified as primary, secondary, or tertiary depending on the number ofnon-hydrogen substituents bonded to the nitrogen atom of the aminogroup. Monoethanolamine (HOCH₂CH₂NH₂) is an example of a well-knowprimary alkanolamine. Widely used secondary alkonalamine includediethanolamine ((HOCH₂CH₂)₂NH). Triethanolamine ((HOCH₂CH₂)₃N) andmethyldiethanolamine ((HOCH₂CH₂)₂NCH₃) are examples of tertiaryalkanolamines which have been used to absorb carbon dioxide fromindustrial gas mixtures. Molecular structures of sterically hinderedamines are generally similar to those of amines, except stericallyhindered amines have an amino group attached to a bulky alkyl group. Forexample, 2-amino-2-methyl-1-propanol (NH₂—C(CH₃)₂CH₂OH).

With primary and secondary alkanolamines (Pinola et al. Simulation ofpilot plant and industrial CO₂-MEA absorbers, Gas Separation &Purification, 7(1), 1993; Barth et al., Kinetics and mechanisms of thereactions of carbon dioxide with alkanolamines; A discussion concerningthe cases of MDEA and DEA, Chemical Engineering Science, 39(12), pp.1753-1757, 1984) the nitrogen reacts rapidly and directly with carbondioxide to bring the carbon dioxide into solution according to thefollowing reaction sequence:

2RNH₂+CO₂

RNHCOO⁻+RNH₃ ⁺  (1)

where R is an alkanol group. This reaction is the cornerstone of thepresent invention, as it is the one accelerated by carbonic anhydrase.The carbamate reaction product (RNHCOO⁻) must be hydrolysed tobicarbonate (HCO₃ ⁻) according to the following reaction:

RNHCOO⁻+H₂O

RNH₂+HCO₃ ⁻  (2)

In forming a carbamate, primary and secondary alkanolamine undergo afast direct reaction with carbon dioxide which makes the rate of carbondioxide absorption rapid. In the case of primary and secondaryalkanolamines, formation of carbamate (reaction 1) is the main reactionwhile hydrolysis of carbamate (reaction 2) hardly takes place. This isdue to stability of the carbamate compound, which is caused byunrestricted rotation of the aliphatic carbon atom around theaminocarbamate group. According to U.S. Pat. No. 4,814,104 the overallreaction for the alkanolamines is written as:

2RNH₂+CO₂

RNHCOO⁻+RNH₃ ⁺  (3)

For the sterically hindered amines both reactions 1 and 2 play majorroles on the CO₂ absorption process. In contrast with the alkanolamines,the rotation of the bulky alkyl group around the aminocarbamate group isrestricted in sterically hindered amines. This results in considerablylow stability of the carbamate compound. The carbamate compound is thuslikely to react with water and forms free amine and bicarbonate ions(reaction 2). Due to the occurrence of reaction 2, only 1 mol of thesterically hindered amine instead of 2 mol of alkanolamine is requiredto react with 1 mol of CO₂. The overall reaction for sterically hinderedamines can be written as (Veawab et al., “Influence of processparameters on corrosion behaviour in a sterically hindered amine-CO₂system”, Ind. Eng. Chem. Res., V 38, No. 1; 310-315; 1999; Park et al.,Effect of steric Hindrance on carbon Dioxide Absorption into New AmineSolutions: Thermodynamic and Spectroscopic Verification and NMRAnalysis, Environ. Science Technol. 37, pp. 1670-1675, 2003; Xu,Kinetics of the reaction of carbon dioxide with2-amino-2-methyl-1-propanol solutions, Chemical Engineering Science,51(6), pp. 841-850, 1996):

RNH₂+CO₂+H₂O

RNH₃+HCO₃ ⁻  (4)

Unlike primary and secondary alkanolamines, tertiary alkanolaminescannot react directly with carbon dioxide, because their amine reactionsite is fully substituted with substituent groups. Instead, carbondioxide is absorbed into solution by the following slow reaction withwater to form bicarbonate (U.S. Pat. No. 4,814,104; Ko, J. J. et al.,Kinetics of absorption of carbon dioxide into solutions ofN-methyldiethanolamine+water, Chemical Engineering Science, 55, pp.4139-4147, 2000; Crooks, J. E. et al., Kinetics of the reaction betweencarbon dioxide and tertiary amines, Journal of Organic Chemistry, 55(4),1372-1374, 1990; Rinker, E. B. et al., Kinetics and modelling of carbondioxide absorption into aqueous solutions of N-methyldiethanolamine,Chemical Engineering Science, 50(5), pp. 755-768, 1995):

R₃N+CO₂+H₂O

HCO₃ ⁻+R₃NH⁺  (5)

Physical absorption enables CO₂ to be physically absorbed in a solventaccording to Henry's law. Such absorption is temperature and pressuredependent. It is usually used at low temperature and high pressures.Typical solvents are dimethylether of polyethylene glycol and coldmethanol.

In recent years, a lot of effort has been put to develop new absorptionsolutions with enhanced CO₂ absorption performance. The use ofsterically hindered amines, including aminoethers, aminoalcohols,2-substituted piperidine alcohols and piperazine derivatives, insolution to remove carbon dioxide from acidic gases by scrubbing processwas the object of a patent in the late 1970 (U.S. Pat. No. 4,112,052).Yoshida et al. (U.S. Pat. No. 5,603,908) also used hindered amines toremove CO₂ from combustion gases, but mainly focused on reducing theenergy consumption from the amines regeneration. Fujii et al. (U.S. Pat.No. 6,274,108) used MEA in a process to absorb CO₂ from combustionexhaust gases, but were more concerned about the plant design, morespecifically storage of the amines and replenishing system. Instead ofusing amines, Suzuki et al. used various formulations of amino-amides toremove carbon dioxide from gases and absorbent (U.S. Pat. No.6,051,161).

In literature, some have reported new formulations of absorptionsolutions for chemical and physical processes. Reports exist about thereduction of corrosion of carbon steel with the use of certain aminecompounds (U.S. Pat. No. 6,689,332). These new formulations may implymixtures of amines (chemical solvent). For instance, U.S. Pat. No.5,246,619 discloses a way of removing acid gases with a mixture ofsolvents comprising methyldiethanolamine and methylmonoethanolamine.Mixtures of dialkyl ethers of polyethylene glycol (physical solvent)(U.S. Pat. No. 6,203,599), and mixtures of chemical and physicalsolvents are reported. GB 1102943, for instance, reports a way ofremoving CO₂ by using a solution of an alkanolamine in a dialkyl etherof a polyalkylene glycol, while U.S. Pat. No. 6,602,443 reduces CO₂concentration from gas by adding tetraethylene glycol dimethyl ether incombination with other alkyl ethers of alkylene glycols. Although U.S.Pat. No. 6,071,484 describes ways to remove acid gas with independentultra-lean amines, mention is also made that a mixture of amines andphysical absorbents can also be used with similar results.

In order to increase the rate of CO₂ absorption, especially for aqueoustertiary alkanolamine solutions, promoters have been added to thesolutions. Promoters such as piperazine, N,N-diethyl hydroxylamine oraminoethylethanolamine (AEE), is added to an absorption solution(chemical or physical solvent). Yoshida et al. (U.S. Pat. No. 6,036,931)used various aminoalkylols in combination with either piperidine,piperazine, morpholine, glycine, 2-methylaminoethanol,2-piperidineethanol or 2-ethylaminoethanol. EP 0879631 discloses that aspecific piperazine derivative for liquid absorbent is remarkablyeffective for the removal of CO₂ from combustion gases. Peytavy et al.(U.S. Pat. No. 6,290,754) used methyldiethanolamine with an activator ofthe general formula H₂N—C_(n)H_(n)—NH—CH₂—CH₂OH, where n represents aninteger ranging from 1 to 4. U.S. Pat. No. 6,582,498 describes a wiresystem to reduce CO₂ from gases where absorbent amine solutions and thepresence of an activator are strongly suggested. U.S. Pat. No. 4,336,233relates to a process for removing CO₂ from gases by washing the gaseswith absorbents containing piperazine as an accelerator. Nieh (U.S. Pat.No. 4,696,803) relied on aqueous solution of N-methyldiethanolamine andN,N-diethyl hydroxylamine counter currently contacted with gases toremove CO₂ or other acid gases. Kubek et al (U.S. Pat. No. 4,814,104)found that the absorption of carbon dioxide from gas mixtures withaqueous absorbent solutions of tertiary alkanolamines is improved byincorporating at least one alkyleneamine promoter in the solution.

Other ways of enhancing CO₂ absorption involve ionic liquids, morespecifically a liquid comprising a cation and an anion having acarboxylate function (US 2005/0129598). Bmim-acetate and hmim-acetateare cited as examples.

Mention of enzyme utilization for gas extraction can also be found inthe literature (U.S. Pat. No. 6,143,556, U.S. Pat. No. 4,761,209, U.S.Pat. No. 4,602,987, U.S. Pat. No. 3,910,780). Bonaventura et al. (U.S.Pat. No. 4,761,209) used carbonic anhydrase immobilized in a porous gelto remove CO₂ in an underwater rebreathing apparatus. Carbonic anhydrasecan also be used to impregnate membranes used to facilitate CO₂ transferinto water for similar purposes (U.S. Pat. No. 4,602,987, U.S. Pat. No.3,910,780). Efforts were made to ensure that the active site of theenzymes fixed on the membranes were in direct contact with the gas phasesubstrate to increase the activity of the enzymes (U.S. Pat. No.6,143,556). This patent is the direct continuation of U.S. Pat. No.6,524,843, which claimed a way to remove CO₂ from gases with an enzyme,the carbonic anhydrase. This new patent aims at improving the CO₂absorption of the previous patent through the additional use ofsolvents, increasing the performance of the bioreactor.

CO₂ transformation may be catalyzed by a biocatalyst. The biocatalyst ispreferably the enzyme carbonic anhydrase. CO₂ transformation reaction isthe following:

CO₂+H₂O

HCO₃ ⁻+H⁺  (6)

Under optimum conditions, the turnover rate of this reaction may reach1×10⁶ molecules/second (Khalifah, R and Silverman D. N., Carbonicanhydrase kinetics and molecular function, The Carbonic Anhydrase,Plenum Press, New York, pp. 49-64, 1991).

SUMMARY OF THE INVENTION

A first object of the present invention is to provide a CO₂ absorptionsolution with an increased CO₂ absorption rate.

In accordance with the present invention, that object is achieved with aformulation for absorbing CO₂ containing water, at least one CO₂absorption compound, and carbonic anhydrase as an activator to enhancethe absorption capacity of the CO₂ absorption compound.

A CO₂ absorption compound in accordance with the present inventionrepresents any compound known in the field which is capable to absorbgaseous CO₂.

Preferably, the CO₂ absorption compound is selected from the groupconsisting of amines, alkanolamines, dialkylether of polyalkyleneglycols and mixtures thereof.

By “amines” (as also in the term “alkanolamines”), it is meant anyoptionally substituted aliphatic or cyclic amines or diamines.

More preferably, the amines are selected from the group consisting ofpiperidine, piperazine and derivatives thereof which are substituted byat least one alkanol group.

By “alkanol”, as in the terms “alkanol group” or “alkanolamines”, it ismeant any optionally substituted alkyl group comprising at least onehydroxyl group.

Advantageously, the alkanolamines are selected from the group consistingof monoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP),2-(2-aminoethylamino)ethanol (AEE),2-amino-2-hydroxymethyl-1,3-propanediol (Tris), N-methyldiethanolamine(MDEA) and triethanolamine.

The preferred dialkylether of polyalkylene glycols used according to theinvention are dialkylether of polyethylene glycols. Most preferably, adialkylether of polyethylene glycol is a dimethylether of polyethyleneglycol.

A second object of the invention is to provide a method to activate aCO₂ absorption solution, which comprises the steps of:

-   -   contacting gaseous CO₂ with an aqueous CO₂ absorption solution        containing at least one CO₂ absorption compound; and    -   adding carbonic anhydrase to said CO₂ absorption solution while        it is contacted with said gaseous CO₂.

Carbonic anhydrase is used as an activator to enhance performance ofabsorption solutions (for chemical/physical absorption) for CO₂ capture.

Thus, a third object of the invention concerns the use of carbonicanhydrase as an activator to increase CO₂ absorption rate in an aqueoussolution used for CO₂ absorption.

The enzyme may be one of the constituents of the absorption solution orit can be fixed to a solid substrate (support) such as packing materialonto which the absorption solution, in contact with gaseous CO₂, flows.

The objects, advantages and other features of the present invention willbe better understood upon reading of the following non-restrictivedescription of preferred embodiments thereof, given for the purpose ofexemplification only, with reference to the accompanying figures andexamples.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents the performance, with or without using carbonicanhydrase, of absorption solutions comprising MEA, Tris, AMP, AEE, Pz orPEG DME as the CO₂ absorption compound; the performance is expressed asthe relative CO₂ transfer rate of the given solution to the CO₂ transferrate of a MEA solution without carbonic anhydrase, the concentration ofthe absorption solutions is 1.2×10⁻² M.

FIG. 2 represents the performance, with or without using carbonicanhydrase, of absorption solutions comprising MEA, AMP, MDEA or Tris asthe absorption compound; the performance is expressed as the relativeCO₂ transfer rate of the given solution to the CO₂ transfer rate of aMEA solution without carbonic anhydrase; the concentration of theabsorption solutions is 1.44×10⁻¹ M.

FIG. 3 represents the performance, with or without using carbonicanhydrase, of absorption solutions comprising MEA or AMP as theabsorption compound; the performance is expressed as the relative CO₂transfer rate of the given solution to the CO₂ transfer rate of a MEAsolution without carbonic anhydrase. the concentration of the absorptionsolutions is 0.87×10⁻¹ M.

DESCRIPTION OF PREFERRED EMBODIMENTS

The activation of an absorption solution by carbonic anhydrase may beobtained (1) by directly adding carbonic anhydrase to the absorptionsolution or (2) by contacting an absorption solution, in contact with agas phase containing CO₂, to a solid support having immobilized carbonicanhydrase.

Carbonic anhydrase enhances performance of absorption solutions byreacting with dissolved CO₂, maintaining a maximum CO₂ concentrationgradient between gas and liquid phases and then maximizing CO₂ transferrate.

The following examples present the two ways to activate absorptionsolutions with carbonic anhydrase.

Example 1

An experiment was conducted in an absorption column. The absorptionsolution is an aqueous solution of2-amino-2-hydroxymethyl-1,3-propanediol (0.15% (w/w)). This absorptionsolution is contacted contercurrently with a gas phase with a CO₂concentration of 52,000 ppm. Liquid flow rate was 1.5 L/min and gas flowrate was 6.0 g/min. Gas and absorption solution were at roomtemperature. Operating pressure of the absorber was set at 5 psig. Thecolumn has a 7.5 cm diameter and a 70 cm height. Two tests wereperformed: the first with no activator, the second with carbonicanhydrase. The concentration of carbonic anhydrase is adjusted to 20 mgper liter of solution.

The results obtained showed that CO₂ removal rate is 1.5 time higher inthe absorption solution containing carbonic anhydrase. CO₂ transfer ratewas equal to 2.3×10⁻³ mol/min with carbonic anhydrase.

Example 2

A gas, containing CO₂ at a concentration of 8% (v/v) is fed to a packedbed reactor containing immobilized carbonic anhydrase. The solidsubstrate is a polymeric material. The gas is countercurrently contactedto an aqueous absorption solution. Impact of the presence of theimmobilized enzyme, as an activator, has been tested for chemical andphysical solvents. Selected compounds for absorption solutions aremonoethanolamine (MEA), piperazine (Pz), 2-amino-2-methyl-1-propanol(AMP), 2-(2-aminoethylamino)ethanol (AEE),2-amino-2,hydroxymethyl-1,3-propanediol (Tris) and dimethyl ether ofpolyethylene glycol (PEG DME). Solutions were prepared at aconcentration of 1.2×10⁻² M.

Operating conditions were the following: gas flow rate is 3.0 g/min,absorption solution flow rate is 0.5 L/min. Height of packing withimmobilized enzyme 75 cm. Operating pressure is 1.4 psig.

Performance of absorption solutions are shown in FIG. 1. Performance isexpressed as a relative CO₂ transfer rate:

${Performance} = \frac{{CO}_{2}\mspace{14mu} {transfer}\mspace{14mu} {rate}\mspace{14mu} {of}{\mspace{11mu} \;}a\mspace{14mu} {given}\mspace{14mu} {solution}}{{CO}_{2}\mspace{14mu} {transfer}\mspace{14mu} {rate}\mspace{14mu} {of}\mspace{14mu} {MEA}\mspace{14mu} {solution}\mspace{14mu} {without}\mspace{14mu} {carbonic}\mspace{14mu} {anhydrase}}$

From FIG. 1, it can be observed that carbonic anhydrase enhanced the CO₂absorption of both chemical and physical absorption solutions.

Example 3

A gas, containing 8% of CO₂ (v/v) is fed to a packed bed reactorcontaining immobilized carbonic anhydrase. The solid substrate is apolymeric material. The gas is countercurrently contacted to an aqueousabsorption solution. Selected compounds for absorption solutions aremonoethanolamine (MEA), 2-amino-2-methyl-1-propanol (AMP),methyldiethanolamine (MDEA) and 2-amino-2,hydroxymethyl-1,3-propanediol(Tris). Solutions were prepared at a concentration of 1.44×10⁻¹ M.

Operating conditions were the following: gas flow rate is 1.0 g/min,absorption solution flow rate is 0.5 L/min. Height of packing is 25 cm.Operating pressure is 1.4 psig.

Performance of absorption solutions are shown in FIG. 2. Performance isexpressed as a relative CO₂ transfer rate:

${Performance} = \frac{{CO}_{2}\mspace{14mu} {transfer}\mspace{14mu} {rate}\mspace{14mu} {of}\mspace{14mu} a\mspace{14mu} {given}\mspace{14mu} {solution}}{{CO}_{2}\mspace{14mu} {transfer}\mspace{14mu} {rate}\mspace{14mu} {of}\mspace{14mu} {MEA}\mspace{14mu} {solution}\mspace{14mu} {without}\mspace{14mu} {carbonic}\mspace{14mu} {anhydrase}}$

From FIG. 2, it can be observed that carbonic anhydrase increased CO₂absorption for all solutions, except for the MEA solution. The absenceof increase between the test with and without enzyme is due to the factthat the efficiency of the MEA solution was of 100% under theseconditions. In this particular example, a relative transfer rate of 1equals to 100% CO₂ removal.

Example 4

A gas, containing 8% of CO₂ (v/v) is fed to a packed bed reactorcontaining immobilized carbonic anhydrase. The solid substrate is apolymeric material. The gas is countercurrently contacted to an aqueousabsorption solution. Selected compounds for absorption solutions aremonoethanolamine (MEA) and 2-amino-2-methyl-1-propanol (AMP). Solutionswere prepared at a concentration of 87 mM.

Operating conditions were the following: gas flow rate is 3.0 g/min,absorption solution flow rate is 0.5 L/min. Height of packing is 25 cm.Operating pressure is 1.4 psig.

Performance of absorption solutions are shown in FIG. 3. Performance isexpressed as a relative CO₂ transfer rate:

${Performance} = \frac{{CO}_{2}\mspace{14mu} {transfer}\mspace{14mu} {rate}\mspace{14mu} {of}\mspace{14mu} a\mspace{14mu} {given}\mspace{14mu} {solution}}{{CO}_{2}\mspace{14mu} {transfer}\mspace{14mu} {rate}\mspace{14mu} {of}\mspace{14mu} {MEA}\mspace{14mu} {solution}\mspace{14mu} {without}\mspace{14mu} {carbonic}\mspace{14mu} {anhydrase}}$

It can clearly be seen that carbonic anhydrase increases the absorptioncapacity of absorption solutions. This increase can be obtained both foramine-based chemical absorption solutions and physical solutions.Reduced costs with lower need for solvents could thus be obtained.

Although preferred embodiments of the present invention have beendescribed in detail herein and illustrated in the accompanying drawings,it is to be understood that the invention is not limited to theseprecise embodiments and that various changes and modifications may beeffected therein without departing from the scope or spirit of thepresent invention.

1. A formulation for catalysis of the reaction CO₂+H₂O

HCO₃ ⁻+H⁺, comprising water and at least one reaction compound selectedfrom N-methyldiethanolamine (MDEA), piperazine (PZ),2-(2-aminoethylamino)ethanol (AEE), and 2-amino-2-methyl-1-propanol(AMP), the water and the at least one reaction compound forming asolution; and carbonic anhydrase to catalyze the reaction.
 2. Theformulation of claim 1, wherein the at least one reaction compoundcomprises MDEA.
 3. The formulation of claim 1, wherein the at least onereaction compound comprises PZ.
 4. The formulation of claim 1, whereinthe at least one reaction compound comprises AEE.
 5. The formulation ofclaim 1, wherein the at least one reaction compound comprises AMP. 6.The formulation of claim 1, wherein the carbonic anhydrase is supportedby a support.
 7. The formulation of claim 1, wherein the carbonicanhydrase is immobilised on a support.
 8. The formulation of claim 1,wherein the carbonic anhydrase is a component of the solution.
 9. Theformulation of claim 1, wherein the reaction is a forward reaction forabsorption of CO₂ from a CO₂ containing gas into the solution.
 10. Theformulation of claim 1, wherein the reaction is a backward reaction. 11.A method for catalysis of the reaction CO₂+H₂O

HCO₃ ⁻+H⁺, comprising: providing a formulation in a reactor, theformulation comprising water, at least one reaction compound selectedfrom N-methyldiethanolamine (MDEA), piperazine (PZ),2-(2-aminoethylamino)ethanol (AEE), and 2-amino-2-methyl-1-propanol(AMP), the water and the at least one reaction compound forming asolution, and carbonic anhydrase; and operating the reactor such thatthe carbonic anhydrase catalyzes the reaction relative to the sameformulation without the carbonic anhydrase.
 12. The method of claim 11,wherein the at least one reaction compound comprises MDEA.
 13. Themethod of claim 11, wherein the at least one reaction compound comprisesPZ.
 14. The method of claim 11, wherein the at least one reactioncompound comprises AEE.
 15. The method of claim 11, wherein the at leastone reaction compound comprises AMP.
 16. The method of claim 11, whereinthe carbonic anhydrase is supported by a support.
 17. The method ofclaim 11, wherein the carbonic anhydrase is immobilised on a support.18. The method of claim 11, wherein the carbonic anhydrase is acomponent of the solution.
 19. The method of claim 11, wherein thereactor is a packed reactor.
 20. The method of claim 19, wherein thecarbonic anhydrase is immobilised on a packing within the packedreactor.
 21. The method of claim 19, wherein the carbonic anhydrase is acomponent of the solution.
 22. The method of claim 11, wherein thereaction is a forward reaction for absorption of CO₂ from a CO₂containing gas into the solution.
 23. The method of claim 11, whereinthe reaction is a backward reaction.
 24. A method for catalysis of thereaction CO₂+H₂O

HCO₃ ⁻+H⁺, comprising: providing a formulation in a reactor, theformulation comprising water, at least one secondary or tertiaryalkanolamine reaction compound, the water and the at least one secondaryor tertiary alkanolamine reaction compound forming a solution, andcarbonic anhydrase; and operating the reactor such that the carbonicanhydrase catalyzes the reaction relative to the same formulationwithout the carbonic anhydrase.
 25. The method of claim 24, wherein thecarbonic anhydrase is supported by a support.
 26. The method of claim24, wherein the carbonic anhydrase is immobilised on a support.
 27. Themethod of claim 24, wherein the carbonic anhydrase is a component of thesolution.
 28. The method of claim 24, wherein the reactor is a packedreactor.
 29. The method of claim 28, wherein the carbonic anhydrase isimmobilised on a packing within the packed reactor.
 30. The method ofclaim 28, wherein the carbonic anhydrase is a component of the solution.31. The method of claim 24, wherein the reaction is a forward reactionfor absorption of CO₂ from a CO₂ containing gas into the solution. 32.The method of claim 24, wherein the reaction is a backward reaction.